﻿#include <iostream>
#include <vector>
#include <queue>
using namespace std;

class Solution
{
    int m, n;
    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { 1,-1,0,0 };
public:
    // 1162. 地图分析
    int maxDistance(vector<vector<int>>& grid)
    {
        m = grid.size(), n = grid[0].size();
        vector<vector<int>> dist(m, vector<int>(n, -1));
        queue<pair<int, int>> q;

        for (int i = 0; i < m; ++i)
            for (int j = 0; j < n; ++j)
                if (grid[i][j] == 1)
                {
                    q.push({ i,j });
                    dist[i][j] = 0;
                }

        int ret = -1;
        while (q.size())
        {
            pair<int, int> p = q.front();
            q.pop();
            int a = p.first, b = p.second;
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && dist[x][y] == -1)
                {
                    dist[x][y] = dist[a][b] + 1;
                    q.push({ x,y });
                    ret = max(ret, dist[x][y]);
                }
            }
        }

        return ret;
    }
};

int main()
{
    vector<vector<int>> v{ {1,0,1},{0,0,0},{1,0,1} };
    cout << Solution().maxDistance(v) << endl;

    return 0;
}